To deliver fuel to direct injection internal combustion engines, a fuel rail or tube is often provided. Frequently, the main fuel is gasoline. Current high pressure fuel rail assemblies are made of a stainless steel tube and numerous stainless steel components such as injectors that are tack welded and thermally brazed together into a complete assembly. Current rail operating pressures are around 20 MPa (2900 PSI) maximum. Conventional designs have some difficulty in dealing with a higher maximum pressure of approximately 30 MPa (4400 PSI) and beyond. Such pressures raise concerns as to the integrity and reliability of the brazed joint connection.
One of the concerns on any welded or brazed joint is the inability to easily verify the reliability of the connection. A brazed joint can visually look satisfactory but be compromised due to variations in the braze process. At higher pressures this would raise concerns about rail safety and performance.
Japanese patent Laid-Open No. 2005-69023 for example discloses a tube or rail along which fuel travels under pressure. Through holes are defined in a wall section of the tube. The fuel rail is formed of diverging branch pipes. As with other prior art disclosures, metal fittings are connected to the tube by a brazing step after the metal fittings are inserted into through holes provided in a peripheral wall section of the main rail.
When the fuel rail and fuel injectors are subjected to high pressures in direct injection gasoline engines, for example, there is sometimes a tendency for fuel to leak, especially if a positional accuracy and roughness sealing surfaces are suboptimal. See, e.g., Japanese patent Laid-Open No. 2003-129920. If the fuel rail is assembled by brazing, there may be adverse consequences to dimensional accuracy and predictability adjacent to a fuel injector holder. If tolerances are exceeded, fuel leakage problem may occur. In some situations, it may be difficult to correct out-of-tolerance circumstances because the wall thickness of the rail is prohibitively thick. Additionally, remedial measures may weaken a seal since the brazing filler metal may accumulate at the junction between a seal ring and the injector holder. Surface roughness of a sealing surface may thereby be caused.
Fuel rails made of aluminum for direct-injection internal combustion engines cannot be used where injection pressures may reach 150-250 MPa. This is because the strength of aluminum is low. Further, the fuel rail may have disadvantageous layout characteristics because the wall thickness of the rail must be sufficient to withstand high fuel pressures. Consequently, production costs rise because contact surfaces with fuel must be treated by expensive surface treatment protocols. This may be required if the aluminum fuel rail is sensitive to alcohol and corrosive fuel.
Among the art considered before filing this patent application are: U.S. Pat. Nos. 8,596,246; 8,844,500; 8,844,502; 8,074,624; EP 2284385; and EP 2333302.